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    Help with ST-120 custom build


    Posts : 19
    Join date : 2016-09-11

    Help with ST-120 custom build Empty Help with ST-120 custom build

    Post by ureche on Fri Jan 04, 2019 5:23 pm

    Hello everybody,

    I'm in the process of building a ST120 amp, but kind of "custom", what I mean, I'm going to use VTA driver, OPT Edcor CXPP60-4.2K, PT is a 400-0-55-400v 470ma / 2x 3.15-0-3.15v 6A toroidal transformer. The rest I sourced myself over time.

    I need some help from you guys. I want to start build the power supply, but I have a few doubts.

    The power supply will be 2 x uf5408 on each side, followed by a 6CD3 damper diode (which I want to use as a slow start, actual rectification will be done by the uf5408, or so I think). The damper diode will have a heater transformer of its own (6.3v 5A). CLC filter 40uF -> 2 x 1H 50ohm 250ma or Edcor 2H 18ohm 400ma -> 265uF. The caps will all be rated 400v and I'll use a pair in series. In the primary, there will be a cl90 thermistor, which will be shorted after 30-40 seconds. This way, the thermistor will be cold for the next power up.

    I know that in the ST120, the stock rectifier is 5AR4, which is rated for 250ma. The damper is 350ma.

    From what I read the toroidal has lower secondary R, compared to EI transformers. Mine has about 30ohm from center tap to each side. I don't know the actual specs of the PT used in ST120.

    Because the toroidal small R, I wonder if the damper diode will survive? Or would I need to add a power resistor before the damper diode?


      Current date/time is Sun Jun 16, 2019 5:49 pm